Semiconductor Device Having a Bidirectional Switch and a Passive Electrical Network

ABSTRACT

A device includes a semiconductor body having an active region and a substrate region that is beneath the active region. A bidirectional switch is formed in the semiconductor body having first and second gate structures that are configured to block voltage across two polarities as between first and second input-output terminals that are in ohmic contact with the electrically conductive channel. First and second switching devices are configured to electrically connect the substrate region to the first and second input-output terminals, respectively. A passive electrical network includes a first capacitance connected between a control terminal of the first switching device and the second input-output terminal and a second capacitance connected between a control terminal of the second switching device and the first input-output terminal. The passive electrical network is configured temporarily electrically connect the substrate region to the first and second input-output terminal at different voltage conditions.

TECHNICAL FIELD

The instant application generally relates to semiconductor devices, andmore particularly relates to bidirectional high electron mobilitytransistors.

BACKGROUND

Semiconductor transistors, in particular field-effect controlledswitching devices such as a MISFET (Metal Insulator Semiconductor FieldEffect Transistor), in the following also referred to as MOSFET (MetalOxide Semiconductor Field Effect Transistor) and a HEMT(high-electron-mobility Field Effect Transistor) also known asheterostructure FET (HFET) and modulation-doped FET (MODFET) are used ina variety of applications. An HEMT is a transistor with a junctionbetween two materials having different band gaps, such as GaN and AlGaN.

HEMTs are viewed as an attractive candidate for power transistorapplications, i.e., applications in which switching of substantiallylarge voltages and/or currents is required. HEMTs offer high conductionand low resistive losses in comparison to conventional silicon baseddevices.

HEMTs are commonly formed from III-V semiconductor materials, such asGaN, GaAs, InGaN, AlGaN, etc. In a GaN/AlGaN based HEMT, atwo-dimensional electron gas (2DEG) arises at the interface between theAlGaN barrier layer and the GaN buffer layer. The 2DEG forms the channelof the device instead of a doped region, which forms the channel in aconventional MOSFET device. Similar principles may be utilized to selectbuffer and barrier layers that form a two-dimensional hole gas (2DHG) asthe channel of the device. A 2DEG or a 2DHG is generally referred to asa two-dimensional carrier gas. Without further measures, theheterojunction configuration leads to a self-conducting, i.e.,normally-on, transistor. Normally-off structures are also possible. Inthese cases, measures must be taken to prevent the channel region of anHEMT from being in a conductive state in the absence of a positive gatevoltage.

One application of type III-V semiconductor technology is abidirectional switch. A bidirectional switch is a device that is capableof switching voltages of positive or negative polarity. That is, abidirectional switch is configured to control current flow in bothdirections. A dual gate type III-V semiconductor bidirectional switchcan be realized by providing two HEMT gate structures in series betweentwo electrically conductive terminals that are in contact with thetwo-dimensional carrier gas. The two HEMTs can share the same driftregion (the resistive voltage sustaining part) of the device which meansthe on-state resistance can be approximately half of a conventional backto back device.

One problem associated with bidirectional switches relates to capacitivecoupling between the channel of the device and the underlyingsemiconductor substrate. In conventional unidirectional semiconductorswitching devices, the underlying semiconductor substrate is typicallytied to the reference potential terminal (e.g., the source terminal) ofthe device by substrate contacts. By tying the substrate to a fixedpotential, the problem of capacitive coupling between a floatingsubstrate and the channel is eliminated and hence the reliability andstability of the device operation is improved. The same benefit cannotbe obtained using a simple electrical contact in the case of abidirectional switch because there is not a single terminal that ismaintained at a reference potential in all states of operations; thevoltage polarity across the device changes. Known solutions to thisproblem suffer from various drawbacks.

SUMMARY

A semiconductor device is disclosed. According to an embodiment, thesemiconductor device includes a semiconductor body having an activeregion and a substrate region that is disposed beneath the activeregion. A bidirectional switch is formed in the semiconductor body andis configured to block voltage across two polarities. The bidirectionalswitch includes first and second gate structures that are eachconfigured to control a conductive state of an electrically conductivechannel that is disposed in the upper active region, and first andsecond input-output terminals that are each in ohmic contact with theelectrically conductive channel. A first switching device is configuredto electrically connect the substrate region to the first input-outputterminal. A second switching device is configured to electricallyconnect the substrate region to the second input-output terminal. Apassive electrical network includes a first capacitance and a secondcapacitance. The first capacitance is connected between a controlterminal of the second switching device and the first input-outputterminal. The second capacitance is connected between a control terminalof the first switching device and the second input-output terminal. Thepassive electrical network is configured to temporarily electricallyconnect the substrate region to the second input-output terminal byturning the second switching device on when the second input-outputterminal is at a higher potential than the first input-output terminal.The passive electrical network is configured to temporarily electricallyconnect the substrate region to the first input-output terminal byturning the first switching device on when the first input-outputterminal is at a higher potential than the second input-output terminal.

According to another embodiment, the semiconductor device includes asemiconductor body having an active region and a substrate region thatis disposed beneath the active region. A bidirectional switch is formedin the semiconductor body and is configured to block voltage across twopolarities. The bidirectional switch includes first and second gatestructures that are each configured to control a conductive state of anelectrically conductive channel that is disposed in the upper activeregion, and first and second input-output terminals that are each inohmic contact with the electrically conductive channel. A firstswitching device is configured to electrically connect the substrateregion to the first input-output terminal when turned on. A secondswitching device is configured to electrically connect the substrateregion to the second input-output terminal when turned on. A passiveelectrical network is configured to generate a first substrate referencesignal that turns the second switching device on during a firsttransitional state of the bidirectional switch and to generate a secondsubstrate reference signal that turns the first switching device onduring a second transitional state of the bidirectional switch. Thefirst transitional state is a state when the second input-outputterminal is at a higher potential than the first input-output terminaland the bidirectional switch is turned on, the second transitional stateis a state when the first input-output terminal is at a higher potentialthan the second input-output terminal and the bidirectional switch isturned on.

A method of operating a bidirectional switch is disclosed. Thebidirectional switch is configured to block voltage across twopolarities. The bidirectional switch includes a semiconductor bodyhaving an active region and a substrate region that is disposed beneaththe active region, first and second gate structures that are eachconfigured to control a conductive state of an electrically conductivechannel that is disposed in the upper active region, and first andsecond input-output terminals that are each in ohmic contact with theelectrically conductive channel. According to an embodiment of themethod, the second switching device is used to temporarily electricallyconnect the substrate region to the second input-output terminal duringa first transitional state of the bidirectional switch. The firsttransitional state of the bidirectional switch is a state when thesecond input-output terminal is at a higher potential than the firstinput-output terminal and the bidirectional switch is transitioned fromOFF to ON. A first switching device is used to temporarily electricallyconnect the substrate region to the first input-output terminal during asecond transitional state of the bidirectional switch. The secondtransitional state of the bidirectional switch is a state when the firstinput-output terminal is at a higher potential than the secondinput-output terminal and the bidirectional switch is transitioned fromOFF to ON. Using the first switching device and using the secondswitching device includes turning the first and second switching deviceson using a passive electrical network that that generates a currentpulse from transitioning of the bidirectional switch.

BRIEF DESCRIPTION OF THE DRAWINGS

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts. The features of the various illustrated embodiments can becombined unless they exclude each other. Embodiments are depicted in thedrawings and are detailed in the description which follows.

FIG. 1 illustrates a bidirectional switch with a network of diodesconnected between the input-output terminals of the bidirectional switchand the substrate region of the bidirectional switch, according to anembodiment.

FIGS. 2A and 2B illustrate equivalent circuit schematics of thebidirectional switch in two different operational states, according toan embodiment. FIG. 2A depicts the bidirectional switch in an OFF state.FIG. 2A depicts the bidirectional switch in an ON state.

FIG. 3 illustrates a bidirectional switch with a substrate voltageregulation circuit connected between the input-output terminals of thebidirectional switch and the substrate region of the bidirectionalswitch, according to an embodiment.

FIG. 4 illustrates an equivalent circuit schematic of a bidirectionalswitch with a substrate voltage regulation circuit connected between theinput-output terminals of the bidirectional switch and the substrateregion of the bidirectional switch, according to an embodiment.

FIG. 5 illustrates the various voltages present on the bidirectionalswitch and the substrate voltage regulation circuit during a steady OFFstate of the bidirectional switch, according to an embodiment.

FIG. 6 illustrates the various voltages present on the bidirectionalswitch and the substrate voltage regulation circuit during atransitional state of the bidirectional switch from OFF to ON, accordingto an embodiment.

FIG. 7 illustrates the various voltages present on the bidirectionalswitch and the substrate voltage regulation circuit during a steady ONstate of the bidirectional switch, according to an embodiment.

FIG. 8 illustrates the various voltages present on the bidirectionalswitch and the substrate voltage regulation circuit during atransitional state of the bidirectional switch from OFF to ON, accordingto an embodiment.

DETAILED DESCRIPTION

According to embodiments described herein, a bidirectional switch isdisclosed with substrate voltage regulation circuit connected betweenthe input-output terminals of the bidirectional switch and the substrateregion of the bidirectional switch. The bidirectional switch includesswitching devices (e.g., transistors) that are configured to connect theinput-output terminals of the bidirectional switch to a substrateregion, depending upon the operational state of the bidirectionalswitch. If the bidirectional switch is operating at a first voltagepolarity wherein a second input-output terminal is at a higher potentialthan a first input-output terminal and is transitioned from OFF to ON, afirst switching device electrically connects the substrate region to thesecond input-output terminal. If the bidirectional switch is operatingat a second voltage polarity wherein the first input-output terminal isat a higher potential than the second input-output terminal and istransitioned from OFF to ON, a second switching device electricallyconnects the substrate region to the first input-output terminal.

Advantageously, the bidirectional switch includes a passive electricalnetwork that can provide the necessary control signaling to turn thefirst and second switching devices ON and OFF without any independentbiasing or control signals. That is, the passive electrical network isself-biasing in the sense that it utilizes the same voltages that areapplied across the input-output terminals of the bidirectional switch togenerate the control signaling for the first and second switchingdevices. In one particular example, the passive electrical networkincludes capacitors that are connected in series with the controlterminals of current driven switches. The transition from OFF to ON ofthe bidirectional switch results in a temporary redistribution ofcharges across the capacitor network that causes a current pulse toappear at the control terminal of the appropriate switching device.Advantageously, this solution can be integrated into a single integratedcircuit. For example, a GaN based bidirectional switch can be combinedwith GaN based current driven switching devices and integrally formedcapacitances to provide the complete circuit. This provides a simplerand more cost effective solution in comparison to a technique thatutilizes discrete components and external biasing signals to providesimilar functionality.

Referring to FIG. 1, a bidirectional switch 100 is depicted, accordingto an embodiment. The bidirectional switch 100 is formed in asemiconductor body 102. Generally speaking, the semiconductor body 102region can include a wide variety of semiconductor materials includinggroup IV semiconductor materials such as Silicon (Si), compound group IVsemiconductor materials such as Silicon carbide (SiC) or Silicongermanium (SiGe), and group III-V semiconductor materials such asgallium nitride (GaN), aluminum gallium nitride (AlGaN), indium galliumnitride (InGaN), gallium arsenide (GaAs), aluminum gallium arsenide(AlGaAs), as well as isolation materials such as sapphire, etc.

A top portion of the semiconductor body 102 includes an upper activeregion 104. The upper active region 104 refers to the layers or regionsof the semiconductor body 102 that provide an electrically conductivechannel. For example, in the depicted embodiment, the upper activeregion 104 includes first and second type III-V semiconductor layers106, 108. The second type III-V semiconductor layer 108 is formed from asemiconductor material having a different band gap than the first typeIII-V semiconductor layer 106. For example, the first type III-Vsemiconductor layer 106 can include intrinsic or lightly doped galliumnitride (GaN) and the second type III-V semiconductor layer 108 includealuminum gallium nitride (AlGaN). More generally, any combination oftype III-V semiconductor materials with different metallic contents canbe used to provide a difference in bandgap. Due to the difference inbandgap between the first and second type III-V semiconductor layers106, 108, an electrically conductive two-dimensional charge carrier gaschannel 110 arises near an interface between the first type III-Vsemiconductor layer 106 and the second type III-V semiconductor layer108 due to polarization effects. Alternatively, instead of type III-Vsemiconductor material, the upper active region 104 can include group IVsemiconductor materials such as Silicon (Si), Silicon carbide (SiC),Silicon germanium (SiGe), etc. The materials can be doped to form activedevice regions, e.g., source, drain, collector, emitter, etc., whichprovide a controllable electrically conductive channel in a knownmanner.

A lower portion 112 of the semiconductor body 102 includes variousregions of the semiconductor body 102 that do not directly contribute inan electrical sense to the provision of the electrically conductivechannel 110. In the depicted embodiment, the lower portion 112 of thesemiconductor body 102 includes a substrate region 114, a nucleationlayer 116, and a lattice transition region 117. The substrate region 114can include can be formed from group IV or group III-V semiconductormaterials. For example, according to one embodiment, the substrateregion 114 can be provided by a silicon or silicon based wafer. Thenucleation layer 116, which may include a metal nitride (e.g., AIN), andthe lattice transition region 117, which may include a number ofsemiconductor nitride (e.g., AlGaN) layers with a gradually diminishingmetallic content, are provided on the substrate region 114 to enable theformation of relatively strain and defect free group IV semiconductormaterial thereon. More generally, the substrate region 114 can includeany intrinsic or bulk portion of the substrate that is beneath theactive device regions, and is more conductive than an intermediaryregion that is between the substrate region 114 and the upper activeregion 104.

The bidirectional switch additionally includes first and second gatestructures 118, 120 that are formed on the semiconductor body 102. Thefirst and second gate structures 118, 120 each include an electricallyconductive gate electrode 122, semiconductor body 102. According to oneembodiment, the intermediary regions 124 are configured (e.g., bydoping) to provide an integrated diode in the gate structure. In thecase of a type III-V semiconductor device, the first and second gatestructures 118, 120 may be configured to alter the intrinsicallyconductive state of the two-dimensional charge carrier gas channel110.semiconductor body 102.

The bidirectional switch 100 additionally includes first and secondinput-output terminals 122, 124 that are in ohmic contract with thechannel 110. The ohmic connection can be provided by electricallyconductive contact structures 126 that are formed in the semiconductorbody 102. These contact structures 126 can be formed from conductivemetals, such as tungsten or aluminum, or alternatively can be formedfrom highly-doped monocrystalline or polycrystalline semiconductors.

The bidirectional switch 100 operates as follows. At a first voltagepolarity, in which the second input-output terminal 124 is at a highervoltage than the first input-output terminal 122, voltage blocking isprimarily handled by the first gate structure 118. That is, an “OFF”signal applied to the first gate structure 118 (e.g., 0V, relative tothe first input-output terminal 122) will disrupt the channel 110 andcauses the device to be in a blocking mode. The bidirectional switch 100becomes conductive by applying an “ON” signal (e.g., a positive voltage,relative to the first input-output terminal 122) to the first gatestructure 118, which places the channel 110 in a conductive state. At asecond voltage polarity, in which the first input-output terminal 122 isat a higher voltage than the second input-output terminal 124, theopposite applies. That is, voltage blocking is primarily handled by thesecond gate structure 120. In this way, the bidirectional switch 100 canblock or permit a current to flow in either direction between the firstand second input-output terminals 122, 124. The bidirectional switch 100can have symmetrical voltage blocking capability at either voltagepolarity. Alternatively, the bidirectional switch 100 can be configuredto have a greater voltage blocking capability at one of the two voltagepolarities. This can be achieved by, among other things, adjusting thedistance between the first and second gate structures 118, 120 and thefirst and second input-output terminals 122, 124.

One problem associated with bidirectional switch 100 that are integratedinto a single substrate, as is the case in the device of FIG. 1, is theso-called “common substrate” problem. In the absence of any furthermeasures, there is a parasitic capacitive coupling that occurs betweenthe first and second input-output terminals 122, 124 and the substrateregion 114. In the figure, a first substrate capacitance 128 representsthe parasitic capacitance between the first input-output terminal 122and the substrate region 114, and a second substrate capacitance 130represents the parasitic capacitance between the second input-outputterminal 124 and the substrate region 114. If the substrate region 114is not tied to a fixed potential, the voltages across these parasiticcapacitances can vary during the operation of the device, which maydegrade the channel and affect the switching behavior during operationof the bidirectional switch 100. In a conventional unidirectionaldevice, this problem is typically solved by tying the substrate of thedevice to the same potential as the reference potential terminal (e.g.,the source terminal) and thus shunting the parasitic substratecapacitance. However, this solution is not available in a bidirectionaldevice because there is no dedicated reference potential terminal. Thatis, the first input-output terminal 122 acts as a reference potential atone voltage polarity and the second input-output terminal 124 acts as areference potential at the opposite voltage polarity.

The semiconductor device depicted in FIG. 1 additionally includes anetwork of first and second diodes 132, 134, which represent one knownsolution to the so-called “common substrate” problem. The first andsecond diodes 132, 134 are schematically represented in FIG. 1. Inprinciple, these diodes can be integrally formed in the semiconductorbody 102 and electrically connected in the depicted manner using knowninterconnect techniques. Alternatively, these diodes can be providedusing discrete devices that are separate from the bidirectional switch100. The anode of the first diode 132 is connected to the substrateregion 114 and the cathode of the first diode 132 is connected to thefirst input-output terminal 122. The anode of the second diode 134 isconnected to the substrate region 114 and the cathode of the seconddiode 134 is connected to the second input-output terminal 124.

Referring to FIGS. 2A and 2B, equivalent schematics of the bidirectionalswitch 100 and the network of first and second diodes 132, 134 aredepicted during different modes of operation of the bidirectional switch100. FIG. 2A depicts an equivalent schematic when the bidirectionalswitch 100 is in an OFF state and the second input-output terminal 124is at a higher potential than the first input-output terminal 122. Forexemplary purposes of discussion, a voltage difference 136 of 200V willbe used. FIG. 2B depicts an equivalent schematic when the bidirectionalswitch 100 is transitioned to an ON state after the operational state ofFIG. 2A.

Referring to FIG. 2A, because the bidirectional switch 100 is turnedOFF, the connection between the first and second input-output terminals122, 124 appears as an electrical open. Thus, the voltage difference 136between the first and second input-output terminals 122, 124 is appliedto a voltage divider network that includes the first and secondsubstrate capacitances 130, 128 and the first and second diode 132, 134.At this voltage polarity, the first diode 132 is in forward conductingmode. The voltage 138 across the first substrate capacitance 128corresponds to the forward threshold voltage of the first diode 132, andis therefore very small (e.g., about 1V). The voltage 140 across thesecond substrate capacitance 130 corresponds to the remaining voltagedifference between the first and second input-output terminals 122, 124,and is therefore very large 136 (e.g., about 199V). In other words, thefirst and second diodes 132, 134 are arranged in a way that essentiallyties the first input-output terminal 122 to the substrate potential, andmaintains the entire applied voltage difference 136 between the secondinput-output terminal 124 and the substrate region 114. This conditionis desirable, as it effectively mimics the effect of a substrate contact(minus the forward voltage of one diode) in a unidirectional device.

Referring to FIG. 2B, because the bidirectional switch 100 is turned ON,a conductive connection between the first and second input-outputterminals 122, 124 is provided. Thus, the voltage difference 136 betweenthe first and second input-output terminal 124 changes to 0V. Moreover,this connection reconfigures the voltage divider network that includesthe first and second substrate capacitances 128, 130 and the first andsecond diodes 132, 134. Now, the circuit includes parallel connectedfirst and second substrate capacitances 128, 130 and first and seconddiodes 132, 134. At the instant that the circuit transitions to thisstate, the charges stored in the first and second substrate capacitances128, 130 redistribute throughout the circuit until an equilibriumcondition is reached. However, due to the presence of the first andsecond diodes 132, 134, the charges stored in the first second substratecapacitances 128, 130 are blocked from discharging through the first andsecond input-output terminals 122, 124. Instead, the chargesredistribute until an equilibrium state is reached between the firstsecond substrate capacitances 128, 130. As a result, the voltage 138across the first substrate capacitance 128 corresponds to roughly halfof the previous voltage difference 136 (e.g., about 99V) and the voltage140 across the second substrate capacitance 130 corresponds to roughlyhalf of the previous voltage difference 136 (e.g., about 99V).

Thus, while the network of first and second diodes 132, 134 depicted inFIG. 1 provides desirable substrate shunting behavior in the OFF stateof the bidirectional switch 100, the transition from OFF to ON createsan undesirable condition in which the previously applied voltage isshared across the voltage divider that includes the first and secondsubstrate capacitances 128, 130, and there is no path for the charges todissipate until the device is turned OFF again.

Referring to FIGS. 3 and 4, a semiconductor device is depicted,according to another embodiment. The semiconductor device includes thebidirectional switch 100 that is formed in the semiconductor body 102 asdescribed with reference to FIG. 1. Different to the embodiment of FIG.1, the first and second diodes 132, 134 can be replaced or added inaddition with a substrate voltage control circuit 300. FIG. 3illustrates a substrate configuration of the bidirectional switch 100with the substrate voltage control circuit 300 being schematicallydepicted. FIG. 4 illustrates a complete circuit schematic of the circuitthat includes the bidirectional switch 100 and the substrate voltagecontrol circuit 300.

The substrate voltage control circuit 300 includes first and secondswitching devices 302, 304. The first switching device 302 is connectedbetween the substrate region 114 and the first input-output terminal122. Thus, by turning the first switching device 302 ON, a conductiveelectrical connection is provided between the substrate region 114 andthe first input-output terminal 122. Likewise, the second switchingdevice 304 is connected between the substrate region 114 and the secondinput-output terminal 124. Thus, by turning the second switching device304 ON, a conductive electrical connection is provided between thesubstrate region 114 and the second input-output terminal 124.

The first and second switching devices 302, 304 can be any of a widevariety of electronic switching devices that are configured to completeor remove an electrical connection in response to a control signal.Exemplary switching devices include metal-oxide semiconductor fieldeffect transistors (MOSFETs), insulated gate bipolar transistors(IGBTs), bipolar junction transistors (BJTs), junction field effecttransistors (JFETs), high electron mobility transistors (HEMTs), etc.The first and second switching devices 302, 304 can be formed in a widevariety of semiconductor technologies including type IV semiconductortechnology, e.g., Silicon (Si), Silicon carbide (SiC), Silicon germanium(SiGe) etc., and type III-V semiconductor technology, III-Vsemiconductor technology, e.g., gallium nitride (GaN), gallium arsenide(GaAs), etc.

The first and second switching devices 302, 304 can be voltagecontrolled switching devices. That is, the first and second switchingdevices 302, 304 can provide an electrically conductive connection byapplying a voltage difference 136 between a control terminal (e.g., thegate) and a reference terminal (e.g., the source) of the device.Alternatively, the first and second switching devices 302, 304 can becurrent controlled switching devices. That is, the conductiveelectrically connection is achieved by injecting current into thecontrol terminal of the device.

As can be seen, each of the first and second switching devices 302, 304may include a reverse conducting diode 306 that is connectedantiparallel to the conduction path of the switching device. Thisreverse conducting diode 306 may be inherent to the structure of theswitching device 302 and 304. For example, in the case of a typicalsilicon based MOSFET device, the body diode that intrinsically arises atthe p-n junction between the body and source regions can provide thisreverse conducting diode 306. Alternatively, the reverse conductingdiode 306 may be separately incorporated into the device.

According to an embodiment, the first and second switching devices 302,304 are integrated into the same semiconductor body 102 as thebidirectional switch 100. That is, the first and second switchingdevices 302, 304 and the bidirectional switch 100 form a singleintegrated circuit. Depending on the technology employed, the first andsecond switching devices 302, 304 can be provided directly beneath theupper active region 104. Alternatively, the first and second switchingdevices 302, 304 can be formed in region of the semiconductor body 102(not shown) that is laterally adjacent to the bidirectional switch 100.In one particular embodiment, the bidirectional switch 100 is a typeIII-V semiconductor device (as shown in the figure) and the first andsecond switching devices 302, 304 are also type III-V semiconductordevices that are incorporated into the same semiconductor body 102. Forexample, the first and second switching devices 302, 304 can be GaNbased HEMTs devices that are incorporated into the same substrate as aGaN based bidirectional switch 100. In one more particular embodiment,the first and second switching devices 302, 304 are configured ascurrent controlled switches. This configuration can be achieved byconfiguring the gate structures of the first and second switchingdevices 302, 304 to inject current into the channel of the device.Alternatively, the first and second switching devices 302, 304 can beprovided by discrete components that are separate from the semiconductorbody 102.

The substrate voltage control circuit 300 additionally includes apassive electrical network 301 (identified in FIG. 4) that is connectedto the control terminals of the first and second switching devices 302,304, the substrate region 114, and the first and second input-outputterminals 122, 124. In general, the passive electrical network 301 caninclude any of a wide variety of passive electrical components such asresistors, capacitors, inductors, etc. As used herein, a passiveelectrical component refers to any electrical component that provides aknown IV response that is not controlled by an independent signal.

The passive electrical network 301 includes a first capacitance 308 thatis connected between the control terminal of the second switching device304 and the first input-output terminal 122 and a second capacitance 310that is connected between the control terminal of the first switchingdevice 302 and the second input-output terminal 124.

The first and second capacitances 308, 310 can be provided using avariety of different techniques and structures. For example, the firstand second capacitances 308, 310 can be provided by a parallel-platecapacitor structure that is specifically designed as such. As anotherexample, the first and second capacitances 308, 310 can be provided fromthe parasitic capacitance of a variety of different structures, e.g.,wire connections, transistor devices, etc. that are not necessarilydesigned exclusively to provide the behavior of a capacitor. In eithercase, these structures can be integrated into the same semiconductorbody 102 as the bidirectional switch 100 in a different region (notshown) and electrically connected using known interconnect techniques.Alternatively, the first and second capacitances 308, 310 can beprovided by discrete devices that are external to the semiconductor body102.

The passive electrical network 301 can additionally include a firstvoltage limiting element 312 connected between the substrate region 114and the control terminal of the first switching device 302. The firstvoltage limiting element 312 is configured to limit an input voltageapplied to the first switching device 302 to below a maximum rated inputvoltage of the first switching device 302. The maximum rated inputvoltage corresponds to a value that the first switching device 302 canaccommodate without failure. The first voltage limiting element 312blocks any voltage below the maximum rated input voltage, and beginsconducting once the maximum rated input voltage is reached. According toan embodiment, the first voltage limiting element 312 is a Zener diode,wherein the reverse conducting Zener voltage corresponds to the maximumrated input voltage of the first switching device 302. More generally,the first voltage limiting element 312 can be any kind of voltagelimiting device (e.g., Schottky diode, PIN diode, MOV, etc.) thatprovides similar functionality.

The passive electrical network 301 additionally includes a secondvoltage limiting element 314 connected between the substrate region 114and an input of the first switching device 302. The second voltagelimiting element 314 is configured to limit a voltage applied to thecontrol terminal of the second switching device 304 to below a maximumrated input voltage of the second switching device 304 in a similarmanner as previously described with reference to the first voltagelimiting element 312. Similarly, the second voltage limiting element 314can be a Zener diode, wherein the reverse conducting Zener voltagecorresponds to the maximum rated input voltage of the second switchingdevice 304. Alternatively, the second voltage limiting element 314 canbe any kind of voltage limiting device (e.g., Schottky diode, PIN diode,MOV, etc.) that provides similar functionality.

Advantageously, the passive electrical network 301 of the substratevoltage control circuit 300 is configured to operate the first andsecond switching devices 302, 304 in such a way that alleviates thetrapped charges condition as described with reference to FIG. 2B.Moreover, the passive electrical network 301 is configured to generatethe necessary control signaling to turn the first and second switchingdevices 302, 304 ON and OFF without any external or independentsignaling. Instead, the control signaling is derived from the voltagesthat are applied across the first and second input-output terminals 122,124.

In a first transitional state of the bidirectional switch 100 at whichthe second input-output terminal 124 is at a higher potential than thefirst input-output terminal 122 and the bidirectional switch 100 istransitioned from OFF to ON (i.e., the condition described withreference to FIG. 1), the passive electrical network 301 generates afirst substrate reference signal that, at least temporality, turns thesecond switching device 304 ON. As a result, a short circuit path existsfor the charges stored in the first and second substrate capacitances128, 130 to dissipate. In a second transitional state of thebidirectional switch 100 at which the first input-output terminal 122 isat a second potential than the first input-output terminal 122 and thebidirectional switch 100 is transitioned from OFF to ON, the passiveelectrical network 301 generates a second substrate reference signalthat, at least temporality, turns the first switching device 302 ON.Again, this creates short circuit path that allows the charges stored inthe first and second substrate capacitances 128, 130 to dissipate.

A working example of how the passive electrical network 301 generatesthe first substrate reference signal during the first transitional statewill now be discussed with reference to FIGS. 5-8. Each of these figurescontain a complete circuit schematic of the circuit that includes thebidirectional switch 100 and the substrate voltage control circuit 300.

Referring to FIG. 5, the first gate structure 118 is turned OFF, and thesecond gate structure is either ON or OFF. As a result, thebidirectional switch 100 is in an OFF state and can maintain a voltagedifference across the first and second input-output terminals 122, 124.In this example, a voltage difference is applied to the input-outputterminals such that the second input-output terminal 124 as at a higherpotential than the first input-output terminal 122. For the exemplarypurposes of discussion, a voltage difference of 400 V will be used. This400V is applied across the voltage divider network formed by the firstand second substrate capacitances 128, 130 and the substrate voltagecontrol circuit 300. The voltage across the gate and reference terminalof the first switching device 302 is slightly below the thresholdvoltage of the gate diode of the first switching device 302. Thus, thefirst switching device 302 is turned OFF. Because the first switchingdevice 302 has a reverse conducting diode 306 that is forward conductingat this bias polarity, the voltage across the first substratecapacitance 128 corresponds to the forward conducting voltage (i.e., theforward threshold voltage) of the reverse conducting diode 306 of thefirst switching device 302. As an example, this voltage is 1 V. Theremaining 399 V is applied across the second substrate capacitance 130.In addition, this voltage is applied across the second capacitance 310and the second switching device 304, which are in parallel with thesecond substrate capacitance 130. In other words, the substrate voltagecontrol circuit 300 produces a voltage divider condition similar to thatdescribed with reference to FIG. 2A.

Referring to FIG. 6 the bidirectional switch 100 is transitioned fromOFF to ON after being in the previous bias condition described withreference to FIG. 5. This transition occurs by applying the necessarysignals to turn the first and second gate structures 118, 120 ON. Thus,a low resistance connection forms between the first and secondinput-output terminals 122, 124 and the voltage across the first andsecond input-output terminals 124 drops from 400V to approximately 0V.Once this happens, the charges stored in the first substrate capacitance128 and the second capacitance 310 redistribute throughout the circuitvia the channel 110. In particular, this redistribution of chargesoccurs causes the first capacitance 308 to charge. The charging of thisfirst capacitance 308 results in a temporary current being present atthe control terminal of the second switching device 304. Because thesecond switching device 304 is a current controlled switch, this currentis sufficient to temporarily place the second switching device 304 in anON state. Once the second switching device 304 is turned ON, it providesa short circuit path for the charges stored in the first and secondsubstrate capacitances 128, 130 as well as other associated capacitancesin the reverse conducting diode 306 and t the second capacitance 310 todissipate via the first and second input-output terminals 122, 124.Thus, different to the scenario described with reference to FIG. 2B inwhich the charges stored across the first and second substratecapacitances 128, 130 are blocked by the first and second diodes 132,134, the second switching device 304 provides an alternate path forthese charges to discharge.

Referring to FIG. 7, a steady ON state of the bidirectional switch 100is depicted. In the steady ON state of the bidirectional switch 100, thecontrol terminal voltage of the first switching device 302 ispractically at zero volts and the control terminal of the secondswitching device 304 is below its threshold voltage. Because the secondswitching device 304 is controlled by a temporary current provided bythe first capacitance 308, the second switching device 304 was only inthe ON state temporarily while the bidirectional switch 100 transitionsfrom OFF to ON. Once the first capacitance 308 is no longer charging,the current at the control terminal of the second switching device 304will subside and the second switching device 304 will automatically turnoff. The temporary ON state condition of the second switching device 304may not necessarily discharge all charges stored in the first and secondsubstrate capacitances 128, 130. In some cases, a minimal voltage (e.g.,15V or less) may remain across first and second substrate capacitances128, 130 while the bidirectional switch 100 is operating in the steadyON state. However, these voltages are low enough to effectivelyeliminate the problems of the fully charged voltage divider conditiondescribed with reference to FIG. 2B. Moreover, the amount of remainingcharges stored (and hence voltage) on the first and second substratecapacitances 128, 130 after the second switching device 304 is turnedOFF can be tuned by altering device parameters of the substrate voltagecontrol circuit 300 such as, capacitance of the first capacitance 308,on-resistance of the second switching device 304, turn-on behavior ofthe second switching device 304, etc.

Referring to FIG. 8, the bidirectional switch 100 is transitioned fromthe ON state to the OFF state by turning the first gate structure 118OFF. The channel 110 of the device is now non-conductive. During thetransitional period from the ON state to the OFF state, the majority ofthe voltage applied to the first and second input-output terminals 122,124 is now distributed across the second substrate capacitance 130, thesecond capacitance 310 and the second switching device 304. Althoughcharging the second capacitance 310, which is in series with the controlterminal of the first switching device 302, temporarily turns the firstswitching device 302 ON and thus temporarily shorts the first substratecapacitance 128, this state will quickly transition to the steady OFFstate once the temporary charging current subsides and the firstswitching device 302 turns OFF. As a result, the voltage distributionwill ultimately revert to the state described with reference to FIG. 5.

The previously described second substrate reference signal is generatedduring the second transitional state, i.e., wherein the firstinput-output terminal 124 is at a higher potential than the secondinput-output terminal 122 and the bidirectional switch 100 istransitioned from OFF to ON, in a corresponding manner using counterpartcomponents of the substrate voltage control circuit 300. To summarize,in the second transitional state, the majority of the voltage differencebetween the first and second input-output terminals 122, 124 (399 Vusing the exemplary values described above) is initially placed acrossthe first substrate capacitance 130. This redistribution of chargesresults in a temporary current at the control terminal of the firstswitching device 302 to alleviate the blocking voltage divider conditionin a similar manner as previously described.

The term HEMT is also commonly referred to as HFET (heterostructurefield effect transistor), MODFET (modulation-doped FET) and MESFET(metal semiconductor field effect transistor). The terms HEMT, HFET,MESFET and MODFET are used interchangeably herein to refer to anyIII-nitride based compound semiconductor transistor incorporating ajunction between two materials with different band gaps (i.e., aheterojunction) as the channel. For example, GaN may be combined withAlGaN or InGaN to form an electron gas inversion region as the channel.The compound semiconductor device may have AlInN/AlN/GaNbarrier/spacer/buffer layer structures. In general, the normally-offcompound semiconductor transistor can be realized using any suitableIII-nitride technology such as GaN that permits the formation ofopposite polarity inversion regions due to piezoelectric effects.

Specifically with regard to GaN technology, the presence of polarizationcharges and strain effects in a GaN-based heterostructure body due topiezoelectric effects yield a two-dimensional charge carrier gas in theheterostructure body characterized by very high carrier density andcarrier mobility. Such a two-dimensional charge carrier gas, such as a2DEG (two-dimensional electron gas) or 2DHG (two-dimensional hole gas),forms the conductive channel of the HEMT near the interface between,e.g., a GaN alloy barrier region and a GaN buffer region. A thin, e.g.1-2 nm, AlN layer can be provided between the GaN buffer region and theGaN alloy barrier region to minimize alloy scattering and enhance 2DEGmobility. In a broad sense, the compound semiconductor transistorsdescribed herein can be formed from any binary, ternary or quaternaryIII-nitride compound semiconductor material where piezoelectric effectsare responsible for the device concept.

Spatially relative terms such as “under,” “below,” “lower,” “over,”“upper,” “above,” “beneath” and the like, are used for ease ofdescription to explain the positioning of one element relative to asecond element. These terms are intended to encompass differentorientations of the device in addition to different orientations thanthose depicted in the figures. Further, terms such as “first,” “second,”and the like, are also used to describe various elements, regions,sections, etc. and are also not intended to be limiting. Like termsrefer to like elements throughout the description.

As used herein, the terms “having,” “containing,” “including,”“comprising” and the like are open-ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a,” “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

Terms such as “same,” “match,” and “matches” as used herein are intendedto mean identical, nearly identical or approximately so that somereasonable amount of variation is contemplated without departing fromthe spirit of the invention. The term “constant” means not changing orvarying, or changing or varying slightly again so that some reasonableamount of variation is contemplated without departing from the spirit ofthe invention. Further, terms such as “first,” “second,” and the likeare used to describe various elements, regions, sections, etc., and arealso not intended to be limiting. Like terms refer to like elementsthroughout the description.

It is to be understood that the features of the various embodimentsdescribed herein may be combined with each other, unless specificallynoted otherwise.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor body comprising an active region and a substrate regionthat is disposed beneath the active region, a bidirectional switchformed in the semiconductor body and comprising first and second gatestructures that are each configured to control a conductive state of anelectrically conductive channel that is disposed in the active region,and first and second input-output terminals that are each in ohmiccontact with the electrically conductive channel; a first switchingdevice configured to electrically connect the substrate region to thefirst input-output terminal; a second switching device configured toelectrically connect the substrate region to the second input-outputterminal; a passive electrical network comprising a first capacitanceand a second capacitance, the first capacitance being connected betweena control terminal of the second switching device and the firstinput-output terminal, the second capacitance being connected between acontrol terminal of the first switching device and the secondinput-output terminal.
 2. The semiconductor device of claim 1, whereinthe first and second switching devices are current controlled switches.3. The semiconductor device of claim 2, wherein the semiconductor bodycomprises a type III semiconductor nitride, wherein the bidirectionalswitch is a high electron mobility transistor, and wherein theelectrically conductive channel is a two-dimensional charge carrier gas.4. The semiconductor device of claim 3, wherein the first and secondswitching devices are high-electron-mobility transistors that areintegrally formed in the semiconductor body.
 5. The semiconductor deviceof claim 1, wherein the first capacitance is exclusively connectedbetween the control terminal of the second switching device and thefirst input-output terminal, and wherein the second capacitance isexclusively connected between the control terminal of the firstswitching device and the second input-output terminal.
 6. Thesemiconductor device of claim 1, wherein the passive electrical networkfurther comprises: a first voltage limiting element connected betweenthe substrate region and an input of the first switching device; and asecond voltage limiting element connected between the substrate regionand an input of the first switching device.
 7. The semiconductor deviceof claim 1, wherein the first and second switching devices areintegrated within the semiconductor body.
 8. The semiconductor device ofclaim 7, wherein the passive electrical network is integrated within thesemiconductor body and is exclusively connected to the first and secondinput-output terminals, the first and second switching devices and thesubstrate region.
 9. A semiconductor device, comprising: a type IIIsemiconductor nitride body comprising an active region and a substrateregion that is disposed beneath the active region, a bidirectionalswitch formed in the type III semiconductor nitride body and comprising:first and second gate structures that are each configured to control aconductive state of an electrically conductive channel that is disposedin the active region, and first and second input-output terminals thatare each in ohmic contact with the electrically conductive channel; afirst current controlled switch configured to electrically connect thesubstrate region to the first input-output terminal; a second currentcontrolled switch configured to electrically connect the substrateregion to the second input-output terminal; a passive electrical networkcomprising a first capacitance and a second capacitance, the firstcapacitance being connected between a control terminal of the secondcurrent controlled switch and the first input-output terminal, thesecond capacitance being connected between a control terminal of thefirst current controlled switch and the second input-output terminal.10. The semiconductor device of claim 9, wherein the bidirectionalswitch is a high electron mobility transistor, and wherein theelectrically conductive channel is a two-dimensional charge carrier gas.11. The semiconductor device of claim 10, wherein the first and secondcurrent controlled switches are high-electron-mobility transistors thatare integrally formed in the type III semiconductor nitride body. 12.The semiconductor device of claim 9, wherein the first capacitance isexclusively connected between the control terminal of the second currentcontrolled switch and the first input-output terminal, and wherein thesecond capacitance is exclusively connected between the control terminalof the first current controlled switch and the second input-outputterminal.
 13. The semiconductor device of claim 9, wherein the passiveelectrical network further comprises: a first voltage limiting elementconnected between the substrate region and an input of the first currentcontrolled switch; and a second voltage limiting element connectedbetween the substrate region and an input of the first currentcontrolled switch.
 14. The semiconductor device of claim 9, wherein thefirst and second current controlled switches are integrated within thetype III semiconductor nitride body.
 15. The semiconductor device ofclaim 14, wherein the passive electrical network is integrated withinthe type III semiconductor nitride body and is exclusively connected tothe first and second input-output terminals, the first and secondcurrent controlled switches and the substrate region.
 16. Asemiconductor device, comprising: a semiconductor body comprising anactive region and a substrate region beneath the active region; abidirectional switch formed in the semiconductor body and comprisingfirst and second gate structures configured to block voltage across twopolarities as between first and second input-output terminals that arein ohmic contact with an electrically conductive channel of thebidirectional switch; first and second switching devices configured toelectrically connect the substrate region to the first and secondinput-output terminals, respectively; and a passive electrical networkcomprising a first capacitance connected between a control terminal ofthe first switching device and the second input-output terminal, and asecond capacitance connected between a control terminal of the secondswitching device and the first input-output terminal, wherein thepassive electrical network is configured temporarily electricallyconnect the substrate region to the first and second input-outputterminals at different voltage conditions.
 17. The semiconductor deviceof claim 16, wherein the first and second switching devices are currentcontrolled switches.
 18. The semiconductor device of claim 17, whereinthe semiconductor body comprises a type III semiconductor nitride,wherein the bidirectional switch is a high electron mobility transistor,and wherein the electrically conductive channel is a two-dimensionalcharge carrier gas.
 19. The semiconductor device of claim 18, whereinthe first and second switching devices are high-electron-mobilitytransistors that are integrally formed in the semiconductor body. 20.The semiconductor device of claim 16, wherein the first and secondswitching devices are integrated within the semiconductor body, andwherein the passive electrical network is integrated within thesemiconductor body and is exclusively connected to the first and secondinput-output terminals, the first and second switching devices and thesubstrate region.